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Fair Value Measurements - Change in Fair Value of Contingent Consideration Obligations (Detail) (USD $)	12 Months Ended
	Sep. 30, 2014	Mar. 31, 2015
Business Combinations [Abstract]
Contingent consideration obligations, Beginning balance	$ 1,595,273us-gaap_BusinessCombinationContingentConsiderationLiability	$ 3,970,931us-gaap_BusinessCombinationContingentConsiderationLiability
Change in fair value of contingent consideration	2,375,658arwr_BusinessCombinationFairValueOfChangeInContingentConsideration
Contingent consideration obligations, Ending balance	$ 3,970,931us-gaap_BusinessCombinationContingentConsiderationLiability	$ 3,970,931us-gaap_BusinessCombinationContingentConsiderationLiability

X

- Definition

Business combination fair value of change in contingent consideration.

+ References

No definition available.

+ Details

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Namespace Prefix:	arwr_
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X

- Definition

Amount of liability recognized arising from contingent consideration in a business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 25

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6408-128476



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 35

-Paragraph 1

-Subparagraph b

-URI http://asc.fasb.org/extlink&oid=6911338&loc=d3e6819-128478

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- Details

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